Field of the Invention
The present invention relates to a job execution device, a non-transitory computer-readable recording medium and a data deletion method which can delete data stored in a storing area so as to be unreadable.
Description of Related Art
In the data deletion executed by using a standard deletion command in an operation system, only the information of the data to be deleted on the management information is deleted. The entity of the data (actual data) is not deleted from a storing medium. Therefore, even though the information of the data does not exist on the management information, the actual data remains in the storing medium. This raises concerns, for example, relating to confidentiality of the information.
In order to delete the information in compliance with the ISO (International Organization for Standardization) standard, it is necessary to overwrite the meaningless data on the actual data which does not exist on the management information but remains in the storing medium, and to make the actual data unreadable. Hereinafter, the process for overwriting the meaningless data is referred to as the overwrite deletion.
As an example for executing the overwrite deletion, for example, in Japanese Patent Application Publication No. 2008-42805, the management table in which the deletion management information for indicating whether the overwrite deletion is necessary for each cluster of the storing unit is registered is provided so as to be separated from FAT (File Allocation Table). In the overwrite deletion process, the overwrite deletion is sequentially executed for the clusters for which the overwrite deletion is necessary, by referring to the management table.
When the releasing request for releasing the area by the standard deletion command or the deletion operation is received from an application program, the deletion management information for the clusters included in the area to be released by the above request is updated on the management table so as to change the information to the necessity of the overwrite deletion. Further, in the FAT, the information is updated so as to change the status of the above clusters to “unused”. Then, in case that the overwrite deletion is executed by referring to the management table, the following trouble is caused. That is, in case that before the overwrite deletion is executed, a new data is written by the application program in the clusters of which the status is set to “unused” on the FAT and for which the deletion management information indicates that the overwrite deletion is necessary on the management table, the overwrite deletion is executed for the new data which is written by the application program.
In another method, when the request for releasing the area is received, the application program is prevented from being executed until the overwrite deletion for all of the clusters to be released by the request is finished. However, in this method, the application program cannot be smoothly executed.
In Japanese Patent Application Publication No. 2008-42805, the execution of the application program is secured. That is, in Japanese Patent Application Publication No. 2008-42805, after the overwrite deletion which is executed in the overwrite deletion process is finished, in the FAT, the information is updated so as to change the status of all of the clusters released by the request to “unused”. As a result, even though the overwrite deletion process is interrupted and the application program is preferentially executed, it is possible to prevent a new data from being written in the clusters for which the overwrite deletion is necessary, before the overwrite deletion is executed.
However, in Japanese Patent Application Publication No. 2008-42805, until the overwrite deletion is finished, the clusters for which the overwrite deletion is necessary are in use on the FAT. Therefore, until the overwrite deletion is finished, a new data cannot be written in the clusters for which the overwrite deletion is necessary. As a result, it is not possible to effectively use the storing medium as a storing resource.
For example, in an MFP (Multifunction Peripheral) which is frequently used, jobs, such as a copy job for writing a file and deleting the written file, and the like, are frequently received. At this time, because the job is executed preferentially over the overwrite deletion process, the clusters for which the overwrite deletion is necessary but for which the overwrite deletion has not been executed (the clusters which are in use on the FAT) are continuously increased. As a result, the storing resource is oppressed, and there is some possibility that the storing area in which a new data can be written (the clusters which are unused on the FAT) is insufficient.
FIG. 16 shows an example of the case in which the storing area in which a new data can be written is insufficient. In the initial state, the storing area which can be used is secured (T1). Next, the new data is written and the storing area is used (T2). Then, the request for releasing the area is received and in the management table, the deletion management information for the clusters to be released by the request is changed to the necessity of the overwrite deletion (T3). At T3, the clusters to be released by the request are still in use on the FAT.
Then, the steps T2 and T3 are repeated without starting the overwrite deletion. Thereby, the clusters for which the overwrite deletion is necessary but for which the overwrite deletion has not been executed (the clusters which are in use on the FAT) are continuously increased. When the storing area in which the new data can be written (the clusters which are unused on the FAT) does not exist (T4), the execution of the job for writing the new data is stopped (T5).
Then, the overwrite deletion is started (T6), and when the storing area which can be used is secured by the area size necessary for the execution of the job (T7), the stopped job is restarted. As described above, the clusters for which the overwrite deletion is necessary but for which the overwrite deletion has not been executed are increased, and when the job cannot be executed, the job must be stopped until the execution of the overwrite deletion is finished.